1. Field of the Invention
The present invention relates to a robot control method, and more in detail, to a robot control method which realizes a profile control on a working object surface for burr removing work or the like.
2. Description of the Related Art
In profiling a curved surface as a working object for working such as burr removing work using an industrial robot, it is sometimes required that, when a tool is pressed to the surface, the force component of the reaction force in, a normal direction to the surface should always be kept constant in order to realize an accurate working.
In order to meet such requirements, the following methods have been executed conventionally;
(1) work is performed while pressing a robot against a working object surface by providing the robot with a constant strength using a mechanical means, or PA1 (2) force which a robot receives from a working object surface or distance between a working object surface and the robot is maintained constant by using a force sensor or a distance sensor. PA1 (1) maintaining at a constant value the absolute value W (=.vertline.&lt;W&gt;.vertline.) of the component &lt;W&gt;, normal to the profiling object plane .left brkt-top., of the force in which the robot RB receives from the profiling object plane .left brkt-top., and PA1 (2) making the Z axis direction of the tool coordinate system coincide with a normal line direction of the profiling object plane .left brkt-top.. PA1 &lt;Zi-1.sup.(0) &gt;; the unit vector in the axial direction of the (i-1)-th joint, expressed by the base coordinate system .SIGMA.0, PA1 &lt;Pn+1.sup.(0) &gt;; the position vector directed from the origin of the base coordinate system .SIGMA.0 to the origin of the coordinate system .SIGMA.n+1 set on the end effector, expressed by the base coordinate system .SIGMA.0, PA1 &lt;Pi-1.sup.(0) &gt;; the position vector directed from the origin of the base coordinate system .SIGMA.0 to the origin of the coordinate system .SIGMA.n+1 set on the (n-1)-th joint, expressed by the base coordinate system .SIGMA.0. PA1 &lt;Fn+1.sup.(0) &gt;; the external force &lt;Fn+1&gt; expressed by the base coordinate system .SIGMA.0, PA1 &lt;Mn+1.sup.(0) &gt;; the moment &lt;Mn+1&gt; expressed by the base coordinate system
However, in the above mentioned method (1), since the normal direction of a curved surface becomes different if the position on the curved surface changes, the force which the robot actually receives changes at every position. As a result, a troublesome minute instruction is required for executing a profile control with high accuracy. Also, in the above mentioned method (2) by using a force sensor for exclusive use, it becomes an issue that the sensor is expensive, peripheral devices such as a mechanism for attaching a sensor and a signal processing circuit are required so that they become obstructive at the time of attaching a large size burr removing working tool, and further, a reliability of the system is influenced by the tolerance of the sensor.